Ice Breaking Vessel

ABSTRACT

An icebreaking vessel ( 10 ) with icebreaking reamers ( 23   a,    23   b ) at each side and, in connection with the reamers, propellers ( 24   a,    24   b ) for the propulsion of the vessel. The icebreaking vessel can be formed by attaching a detachable icebreaking bow section ( 31 ) equipped with reamers and propellers in connection with them to any such ship ( 30 ) which is not an actual icebreaker and which has corresponding joint members for attaching the detachable bow section to the ship.

The object of the present invention is an icebreaking vessel presentedin the introduction to claim 1.

Known icebreaking vessels can have several propellers attached toconventional propeller shafts or to either fixed or azimuthing thrusterapparatuses, and engines driving these. High-powered icebreakers canhave several propellers in the stern. There may be propellers at the bowof a vessel as well. Azimuthing thruster apparatuses improve thevessel's manoeuvring characteristics and ability to increase the widthof the ice channel, for example. The propellers in a thruster can eitherbe pullers or pushers. A single thruster can also have two propellers,which may rotate in opposing directions.

For an icebreaker to create a sufficiently wide channel in the ice, itis a known solution to design a wider bow section of the icebreaker,i.e. equalling the width of the desired channel. The rest of the vesselcan then be narrower, which improves the seaworthiness of the icebreakerin open water conditions. It is furthermore a known solution to equip anicebreaker with reamers, i.e. with widened sections intended to breakthe ice at the edge of the channel even when the vessel proceeds astern.Icebreaking vessels have been presented in publications U.S. Pat. No.4,831,951A, U.S. Pat. No. 5,460,110A and U.S. Pat. No. 3,931,780A.

Similar characteristics can be achieved also in other types of vesselsthan actual icebreakers by attaching a wider, ice-breaking bow sectionto the bow of the vessel. If the vessel is reinforced for ice conditionsand has sufficient engine power, it can manoeuvre in icy conditions andreplace an actual icebreaker, at least if the ice is relatively thin.

A common problem with known icebreaking vessels and icebreakers is,however, that such vessels have difficulties in making turns incompressive ice due to the length of these vessels. An icebreaker inparticular should be as agile as possible to be able to move aboutrapidly in different directions and to effectively assist vessels thathave gotten stuck in ice. If an icebreaker also has bow thrusters, inaddition to the propellers in the stern, the manoeuvring characteristicsof the vessel improve but even so, the icebreaker is not usually capableof sharp turns in compressive ice.

The purpose of the present invention is to create a new type oficebreaking vessel that in several respects is more effective and agilein compressive ice than known icebreaking vessels. Another purpose ofthe invention is to create an icebreaking vessel by attaching a new typeof detachable icebreaking bow to a ship.

An icebreaking vessel according to the invention is characterized inwhat has been presented in the characteristics section of claim 1.

An icebreaking vessel according to the invention has, at each side,downwards breaking reamers in the midship area, or between the midshipand the bow of the vessel. To propulse the vessel, there are propellersin connection with the reamers, which can be attached to the propellershafts directed towards the stern of the vessel. The propeller shaftscan be horizontal or they can be tilted downwards or upwards and, asviewed from above, the propeller shafts can be parallel or they can bedirected outwards, towards the sides of the vessel, or inwards, wherebythe propeller shafts form an angle relative to one another. Thepropellers in connection with the reamers can also be attached to eitherfixed or azimuthing thruster apparatuses. Thruster apparatuses can haveone or two pulling propellers ahead of the thruster apparatus, or one ortwo pusher propellers astern of the thruster apparatus, or at least onepropeller ahead of the thruster apparatus and at least one propellerastern of the thruster apparatus.

Preferably, the downwards breaking reamers at each side of the vesseland the propellers in connection with them are located in the midshiparea, or between the midship and the bow of the vessel. The propellersat each side of the vessel are attached in connection with the reamerssuch that they are located astern of the reamers in the vessel.

Downwards breaking reamers have, on the stern side, a inclinedicebreaking surface rising astern and upwards, due to which it ispreferable to position propellers at the sides of the vessel in thisarea of the reamer. Because the inclined surface in the reamer isprimarily required at the ice to be broken and the propellers arelocated entirely underwater, the attachment point for a propeller shaftor a fixed or azimuthing thruster apparatus arranged in the reamer doesnot necessarily have to be inclined, however. This attachment point canbe, as adapted to the required joint, also a horizontal or verticalplane surface or an otherwise-aligned area of the hull.

It is preferable to position propellers at the sides of the vessel suchthat they are located as close to the outboard edge of the vessel aspossible, but inside the outboard edge, however, such that thepropellers do not touch the pier side while the vessel is moored. Fixedor detachable fenders can naturally be added to the side of the vessel,however, to protect the propellers, which can then be positioned evenvery close to the side of the vessel. Due to the shape of the vesselhull or other reasons, propellers may in some cases be positioned alsosignificantly closer to midship, under the hull of the vessel. In such acase, however, the distance between the propellers becomes smaller,which decreases the torque created by the propellers when turning thevessel. The turning characteristics of the vessel improve when there isa sufficient distance between the propellers in connection with thereamers located on each side.

In some cases, the propellers in connection with the reamers cause theicebreaking vessel to sway slightly from side to side, which may assistthe advance of the vessel in ice. The swaying breaks ice at the sides ofthe vessel, whereby the vessel does not become wedged to a halt in theice channel.

An icebreaking vessel according to the invention can also be equippedwith propellers positioned in connection with reamers at the sides ofthe vessel only. It is possible to design the engines driving thepropeller at the sides with such a high output that the vessel canoperate powered by them only. The thrust force and manoeuvringcharacteristics of an icebreaking vessel according to the invention can,in this way, be adequate without any other propellers. However, otherpropellers can also be added to the vessel, for example such that thereis at least one propeller in the stern of the vessel. In the stern ofthe vessel, there may be one or several propellers attached to propellershafts or thruster apparatuses. An icebreaker equipped with propellersat the sides of the vessel and with at least a single propeller in thestern of the vessel is very effective and capable of agile turns,particularly if the propellers at the sides are driven in oppositedirections.

In order to achieve effective icebreaking characteristics for a vesselaccording to the invention also when turning in severe ice conditions,the inclination of the hull sides relative to the vertical plane in thebow section of the vessel is greater than 10° at the point where thehull sides of the ship touch the ice to be broken. The hull sides of thevessel can in some cases be perpendicular as well, but if more effectiveicebreaking characteristics are required, particularly when the vesselis making a turn, the inclinations of the hull sides can be designed tobe considerably high.

An icebreaking vessel according to the invention can also be arrangedsuch that a ship is attached to a detachable icebreaking bow sectionwith reamers at the sides and propellers in connection with them.

The ship can be an icebreaker, and an upgrade of its icebreakingcapability is accomplished by attaching to it a detachable icebreakingbow section. The objective can be, for example, an improvement in theicebreaking capability of the icebreaker or some other reason. The shipdoes not have to be an icebreaker, however, because the detachableicebreaking bow section can be attached to any type of ship, such as aregular merchant ship or a cargo vessel that is not incapable ofbreaking ice independently. Such a combination results in an icebreakingvessel. A vessel equipped with a detachable bow according to theinvention can be significantly more effective when such a detachableicebreaking bow section with reamers at the sides and propellers inconnection with them is attached to the ship. The total engine power ofthe propellers in connection with the reamers in the detachableicebreaking bow section can be even greater than or equal to the enginepower of the propeller or propellers of the ship that is attached to thedetachable bow section.

Such a solution is particularly advantageous when the aim is to use thevessel in an icebreaking role part of the time and part of the time assuitable for open water conditions. Thus the detachable icebreaking bowsection is attached to the ship when icebreaking is necessary or whenthe ship is headed to ice-covered water areas, and the bow section isdisconnected from the ship when the ship is used in open water areas.The draught of the detachable bow section equipped with reamers andpropellers can be equal to the draught of the ship. Their draughts canalso be non-equal, however. The draught of the detachable bow sectioncan be greater or smaller than the draught of the ship to be attached toit. If the draught of the ship is greater than the draught of thedetachable bow, the ship's hull will function as an ice plow whichdiverts ice to the sides such that it does not reach the sternpropeller.

Preferably, the detachable bow also increases the stability of the shipto be attached to it. If the ship is a short tug which is also used forbreaking ice, for example, the bow of the ship, due to the short lengthof the ship, tends to rise too high while breaking ice. In such a casethe detachable bow will increase the total length of the ship, wherebythe vessel becomes more stable while breaking ice.

The draught and use of space in both the detachable bow section and theship can be adjusted, for example, by distributing parts of thepropulsion system of the detachable icebreaking bow section, for examplean electric motor, generator, diesel engine and the fuel tank of thediesel engine, such that some of the said parts are located in thedetachable icebreaking bow section and some in the vessel.

According to the invention, propellers at the sides of the vessel arehighly preferable because they have a high thrust force in normalconditions, i.e. in open water and in light ice. This is because thepropellers at the sides of the vessel are in open water, whereby theirpropeller wash will not hit the hull of the vessel and thereby reducethe thrust. The propeller wash from propellers located at the sides willalso not hit the propellers in the stern of the vessel, which wouldreduce the thrust from the stern propellers.

Known icebreakers, such as the Finnish icebreaker Urho, have twopropeller shafts directed forward in the ship bow. Thus the propellerwash from these propellers hits the ship bow, which reduces the thrustfrom the propellers. Their propeller wash also hits the sternpropellers, reducing the thrust from the stern propellers as well.Similar disadvantages also result from a vessel having a singleazimuthing thruster apparatus, for example, located in the middle in thebow of the vessel.

Propellers located in the bow of a vessel also limit the optimisation ofthe bow shape. Due to the propellers in the bow, the bow cannot beshaped optimally for breaking ice only, and thus the bow shape of theicebreaker becomes a compromise. Because in a solution according to theinvention, there are no propellers in the bow of the icebreaking vessel,the bow shaped can be freely optimised in the best possible manner interms of breaking ice.

In a solution according to the invention, there are no propellers in thebow of the vessel. The propellers are at the sides of the vessel. Thepropellers on the sides of a vessel according to the invention aresufficiently close to the bow, however, to be able to functioneffectively when encountering ice ridges and heavy channels, andparticularly at the sides of bow, which is the critical area.Positioning the propellers at the sides of the vessel, in connectionwith icebreaking reamers, accomplishes a great benefit in that, in aheavy channel, a ridge and in a compressive ice field, propellers closeto the vessel sides eat up ice, break down the ridge and flush the sidesof the vessel. Propellers at the sides of a vessel will functioneffectively even when they are attached to conventional backwardsdirected propeller shafts and do not point forward.

Propellers at the sides of a vessel decrease the resistance of thevessel, make the channel wider, suck down the ice, and blow away iceblocks. Propellers positioned at the sides also make it easier to widenthe ice channel by means of thruster apparatuses in the stern or therudders, because the propellers at the sides have broken the ice at theedges of the ice channel and the ridge, which are the most taxing areasto clear for an icebreaker. Also heeling the ship is very effective inthis way.

Steeply sloped sides are possible in the optimisation of the bow shapebecause it is the propellers that break up the mass of ice at the sides,not the hull. Propellers at the sides of a vessel jointly with the bowshape and a narrow stern make the turns and heeling of a vesselaccording to the invention more effective than with a ship equipped withnormal reamers.

When manoeuvring the vessel, the propellers at the sides can be rotatedin opposite directions, whereby the large distance between thepropellers creates a large torque resulting in a turning action on thevessel. Simultaneously, the sloped sides of the vessel enable the bow tobreak ice sideways when carrying out a turning manoeuvre. Thus turning avessel according to the invention even in place in severe ice conditionscan be readily accomplished.

The propeller wash from the propellers at the sides of the vessel alsoeffectively suck down ice blocks from under the hull of the vessel tothe sides, where there is clear space. This way, only few ice blocks endup at the stern propellers and their thrust force remains at a goodlevel. Even nozzles and a normal diesel-powered system can be used inthe stern propellers of a vessel according to the invention because theice torques are low in the stern when driving ahead.

Due to what was stated above, any combination of propeller systems canbe installed in the stern of a vessel according to the invention. Thepropulsion equipment in the stern can be, for example, 1 to 3 azimuthingor fixed thruster apparatuses or a single or several combinations of aregular propeller shaft, propeller and rudder.

Driving ahead and manoeuvring a vessel according to the invention can beeffectively accomplished even if it has regular propeller shafts andrudders in the stern. Only the vessel's capability to proceed astern, tomanoeuvre and to spread the channel are improved if the vessel hasazimuthing thruster apparatuses in the stern. To enable heeling, also anormal ducted propeller can be used in the stern, in addition to regularpropulsion, because the shroud will collect only a little ice.

According to the invention, the conventional propeller arrangement ofthe propellers at the sides is preferably suitable for detachable bowsolutions because the solution is inexpensive compared to thrusterapparatuses. The reamer area of the vessel can also be equipped withazimuthing or fixed thruster apparatuses. The additional benefit to behad from them is rather small, however, because regular propeller shaftswork very well in the manner described above.

An icebreaking vessel according to the invention can also be such thatthe vessel has propellers in connection with the reamers only,preferably at the widest point of the vessel. In such a case the vesselhas no other propellers in the stern or bow.

It is preferable according to the invention that the bow section of theicebreaking vessel is as short as possible. The draught of the bowsection of the vessel can be equal to the draught of the stern sectionof the vessel, but the draught of the bow section can also be greater orsmaller than the draught of the stern section.

The frame angles and vertical angles in the bow of the vessel are,particularly in icebreakers, preferably small, i.e. the bow is shapedflat. It is also preferable that the sides of the bow are heavilyinclined and that the bottom rises towards the sides. However, the sidecan in some cases also be vertical and the bottom can be horizontal. Thewide bow section is followed by a reamer breaking heavily downwards inthe midship section of the vessel, in connection with which there is apropeller at both sides of the vessel. On the stern side of the reamer,the waterline of the vessel is narrower and generally narrows downtowards the stern.

A propeller in connection with the reamer has a large propellerclearance, whereby broken ice blocks will not get wedged between thepropeller and the hull. Most preferably, the propeller shafts are angledoutwards and downwards. Such an arrangement is preferable particularlywhen the shaft of a propeller in connection the reamer is coupled in theconventional manner with an engine located in the vessel. The propellersin connection with the reamers can also be attached to fixed orazimuthing thruster apparatuses. The propeller shafts of both thrusterapparatuses can then be separately pivoted either entirely freely orunder limitations.

The shape and rather shallow draught of the bow divert the ice blocksalso under the bottom of the bow section, which is preferred, however,in a solution according to the invention. It is not advisable to installa plow or a similar apparatus under the bottom because it would divertmore ice blocks to the propellers in connection with reamers. In auniform ice sheet and in light channels, the side propellers receivelittle ice only, which is preferable because it is not useful to expendenergy breaking up the ice blocks.

The propeller wash from the propellers in connection with the reamers,located at the sides of the vessel, sucks up ice from under the bottomto the sides, whereby the propellers in the stern preferably only comeinto contact with a small amount of ice blocks while proceeding ahead.

The propeller wash becomes more powerful if the draught of the sternsection of the vessel is smaller, whereby the suction of outboardturning propellers at the sides of the vessel is directed at a suitableheight relative to the bottom of the stern section of the vessel.Propellers turn outboard when in a propeller under the vessel, apropeller blade directed towards the bottom of the vessel moves towardsthe side of the vessel.

According to the invention, the ratio between the power rating of thepropellers at the sides of the vessel and the total power rating of thevessel can vary. If the vessel has no other propellers than thepropellers in connection with the reamers at the sides of the vessel,their power rating equals the total power rating of the vessel. If thereis at least a single propeller in the stern of the vessel, the totalpower rating of the propellers at the sides of the vessel can, forexample, amount to roughly half of the total power rating of the vessel.

In such a case, the impact of ice on the speed remains relatively smalleven in a uniform ice sheet and in light channels. The ratio betweenthese power ratings can also differ from what is presented above,however. Correspondingly, if an icebreaking vessel has been arranged byattaching a detachable bow to a ship that is not an icebreaker, thepower rating of the propellers at the sides of the detachable bow, inconnection with the reamers can, for example, roughly equal the totalpower rating of the propellers in the ship. Even this ratio between thepower ratings can also differ from what is presented above, however.

In a heavy channel and in ice ridges, the purpose of the propellers atthe sides of the vessel is to break up the mass of ice, such ice offfrom the ridge and break up the ridge while at the same time flushingthe sides and blowing the ice mass astern from the ridge. This, combinedwith the thruster apparatuses in the stern or with turning the ruddersto the sides and back, will widen the opening in the ice ridge and breakup the ice ridge.

Heeling can be accomplished effectively because, according to theinvention, the bow section of the vessel is wider and has a round shape.This gives more space for turning the stern section of the vessel.Similarly, because the propellers at the sides of the vessel break theedges of the ridge, heeling can be accomplished very effectively, evenbetter than with known multi-purpose icebreakers.

When surging into a large ice ridge, the bow penetrates deep enough suchthat the impact of the propellers at the sides of the vessel and heelingmake it possible to directly penetrate the ice ridge at a slow speed.This also means that a penetration of an ice ridge is possible even whenthe displacement of the vessel is small. The relatively shallow draughtand the low mid section area coefficient in the bow generally decreasethe resistance, i.e. the volume of ice mass to be displaced isrelatively small.

When proceeding astern with an icebreaking vessel according to theinvention in a uniform ice sheet and in a channel, the propellers inconnection with the reamers come into contact with very little ice. Thusit is not disadvantageous to have the propellers attached to propellershafts and to include propeller skegs.

In a compressive ice field, a wide bow section of the vessel ispreferable because it creates a space in the ice channel before thechannel closes up and the ice presses against the sides of the ship. Thebow section of the vessel only has a short straight portion and heavilyinclined sides. The propellers at the sides break up the pressing massof ice and lubricate the sides. Thus, the performance in a compressiveice field is relatively high even at a low propulsion power.

The broad bow section creates space for turning the vessel. Similarly, achannel wider than the hull of the vessel stern section, created in anuniform ice field, helps to accomplish this. Additionally the heavilyinclined sides of the bow section, small length and the short parallelstraight portions of the sides result in having also the bow sectionbreak ice sideways when the propellers at the sides are driven inopposite directions or at unequal speeds. In such a case, the propellerwash from the side driven astern also breaks up ice and lifts water ontop of the ice. Thus the vessel is highly capable of making turns at asmall radius in a uniform ice field, both bow-first and stern-first.

When towing a ship in the towing notch, the great distance between thepropellers at the sides provides an advantageous manoeuvring torquecompared with traditional icebreakers, which do not have this type ofsolution. Even though the front portion of the bow resists a turn to theside, the side propeller apparatuses in connection with the reamerslighten up the edges of a heavy channel and an ice ridge and flush thesides of the vessel.

When using a detachable bow to create an icebreaking vessel, thethruster vessel can also be a conventional propeller-rudder ship with aclearly shallower draught than a regular icebreaker. In such a case, thedraught of the ship can be smaller than the draught of the detachablebow section.

The propulsion power of the propellers positioned in the detachable bowcan be smaller than, equal to, or greater than the output of thepropulsion equipment in the actual vessel.

If electric motors driven by diesel generators are used as enginesystems in the vessel and/or in the detachable bow, the various parts ofthe engine systems can be distributed in several various ways in thevessel and in the detachable bow section. The propeller is rotated by anelectric motor coupled with it, but the electricity required by theelectric motor can be transmitted by cables from a more distantlocation. This way the electric generators required for electricitygeneration, diesel engines and fuel tanks for the diesel engines can bedistributed as required such that any of these components are either inthe vessel or in the detachable bow section.

In the following, the invention is described using examples withreference to the appended drawings, in which

LIST OF FIGURES

FIG. 1A shows a side view of an icebreaking vessel according to theinvention.

FIG. 1B shows a schematic view of the vessel in FIG. 1A as seen frombelow.

FIG. 2A shows a side view of a ship to which a detachable bow sectioncan be attached.

FIG. 2B shows the vessel in FIG. 2A as seen from below.

FIG. 3A shows a side view of the detachable icebreaking bow section.

FIG. 3B shows a schematic view of the detachable bow section in FIG. 3Aas seen from below.

FIG. 4A shows a side view of the vessel in FIG. 2A and the detachablebow section in FIG. 3A as attached to one another.

FIG. 4B shows a schematic view of the vessel in FIG. 2B and thedetachable bow section in FIG. 3B as attached to one another and seenfrom below.

FIG. 5A corresponds to FIG. 1A and shows another embodiment of theicebreaking vessel.

FIG. 5B shows the vessel in FIG. 5A as seen from below.

FIG. 6A shows a side view of a ship to which a detachable bow sectioncan be attached.

FIG. 6B shows the ship in FIG. 6A as seen from below.

FIG. 7A shows another embodiment of the detachable icebreaking bowsection.

FIG. 7B shows the detachable bow section in FIG. 7A as seen from below.

FIG. 8A shows the ship in FIG. 6A and the detachable bow section in FIG.7A as attached to one another.

FIG. 8B shows the ship in FIG. 6B and the detachable bow section in FIG.7B as attached to one another.

FIG. 9A shows a side view of the vessel in FIG. 8A where the propellersof the detachable bow section are in a pivoted position.

FIG. 9B shows the vessel in FIG. 9A as seen from below.

FIG. 10A shows a schematic back view of the vessel in FIG. 8A.

FIG. 10B shows a schematic back view of the vessel in FIG. 9A.

DESCRIPTION OF THE FIGURES

FIGS. 1A and 1B show an icebreaking vessel 10 according to theinvention. In this example, the icebreaking vessel 10 was built toprimarily function as an icebreaker, as it has a wide bow section 20 toopen up a sufficiently wide lane or channel in the ice for the ships tobe assisted. The stern section 21 is narrower than the bow section 20,whereby the vessel is suitable, due to its seagoing characteristics,also for use in open water conditions. Between the wide bow section 20and the narrower stern section 21 of the vessel 10, on each side of thevessel 10 there are downwards breaking reamers 23 a and 23 b withinclined surfaces rising astern and up, which break up the edges of theice lane when the icebreaker proceeds stern ahead.

According to the invention, propellers 24 a and 24 b are attached inconnection with the reamers 23 a and 23 b at each side of theicebreaking ship 10 shown in FIGS. 1A and 1B. In this example, thepropellers 24 a and 24 b are installed in the conventional manner usingpropeller shafts 25 a and 25 b directed towards the stern section of theship. FIG. 1B is shown schematically such that it also shows thelocations of motors 26 a and 26 b and the directions of the propellershafts 25 a and 25 b.

Most preferably, there is space available for the propellers 24 a and 24b in connection with the reamers and their motors 26 a and 26 b in thebow area, where the hull of the vessel is narrower, but they can also bepositioned in the midship section of the vessel if the hull shape of thevessel allows this. If fixed shaft struts are used in connection withthe propellers 24 a and 24 b, they are most preferably tilted 3°-10° inthe transverse direction of the vessel.

FIG. 1B shows that the propeller shafts 25 a and 25 b are not parallel.They are directed slightly outwards, towards the side of the vessel,such that the propeller shafts 25 a and 25 b together form a smallangle. However, the propeller shafts 25 a and 25 b can also be parallelor tilted inwards, but the arrangement shown in FIG. 1B allows betterfitting of the motors 26 a and 26 b driving the propeller shafts 25 aand 25 b into the hull of the vessel 10. Such an angle between thepropeller shafts 25 a and 25 b is also preferable in some icebreakingconditions. The propellers 24 a and 24 b in connection with the reamersof the vessel can also be attached to other types of propulsionequipment, such as azimuthing thruster apparatuses, as described below.

The vessel 10 shown in FIGS. 1A and 1B has, in its stern, an azimuthingthruster apparatus 27 and a propeller 24 c, whereby all three propellers24 a, 24 b and 24 c can be used for propelling and manoeuvring thevessel 10. A very effective solution for any type of manoeuvring is toenable the thruster apparatus 27 to pivot a full 360° circle and toenable both the propellers 24 a and 24 b at the sides to be usedseparately to propulse the ship ahead or astern. Thanks to the bow shapeof the vessel 10, inclined side shells in the bow and the propellers 24a and 24 b at the sides, rotating in opposing directions, the vessel 10is capable of making a turn in place even in severe ice conditions.

FIGS. 2A and 2B show a ship 30 that can be modified into an icebreakingvessel by means of a detachable bow section 31 shown in FIGS. 3A and 3B.In other respects, the ship 30 does not have to be in any wayspecialised, and it can indeed be a regular merchant or cargo ship.However, the ship must have joint members for attaching the detachablebow section to it. The joint members are not shown in the drawings. Theship can also be ice-reinforced for the most severe conditions.

When a detachable bow section is used, both the ship and the detachablebow section can be optimised for entirely different conditions. The shipcan be shaped and optimised for use in open water, whereby its hull doesnot necessarily have to be reinforced for ice. The detachable bowsection can be shaped and reinforced to operate as an icebreaker. Thusbuilding and operating the vessel and the detachable bow section becomesmore economical. Using a reinforced icebreaking vessel in open waterwould not be economical because an icebreaker has to break up a widechannel. An icebreaker would make a poor cargo vessel.

Attaching a detachable bow section to a vessel designed for open waterdoes not pose a problem because the mechanical joint members can be madereliable using relatively simple structures. The joint members can alsobe made such that they allow variation in the draught of the vessel evenif there is no change in the draught of the detachable bow section. Sucha solution can be preferable when a vessel equipped with a detachablebow section visits a port to unload cargo and returns with thedetachable bow section without any cargo.

When any merchant ships or cargo ships have joint members for attachinga detachable bow section to the ship, any merchant ship or cargo shipcan chosen from a group of two or several ships, and a detachableicebreaking bow section can be attached to it. In such a case it can bearranged that at least two merchant ships or cargo ships alternate toform an icebreaking vessel, each ship having joint members for attachinga detachable icebreaking bow section equipped with reamers andpropellers in connection with them in turns to these ships.

According to the invention, a ship proceeding through the NortheastPassage or a cargo vessel entering a frozen Bothnian Bay, for example,does not require support from an icebreaker because the detachableicebreaking bow section can be attached to the cargo vessel before theship departs for the ice-covered area. When the ship arrives in openwater the detachable bow section can be detached and attached to anothership departing for an ice-covered area. It is much more preferable tomaintain icebreaking bow sections that are available as required than toalways provide an icebreaker to assist the ship.

The detachable bow section 31 attachable to the ship 30 shown in FIGS.3A and 3B corresponds with the bow section of an icebreaker shown inFIGS. 1A and 1B, which is wide enough to open up a channel in ice. Thedetachable bow section 31 is also substantially wider than the ship 30to which it is attached. FIGS. 3A and 3B show that the detachable bowsection 31 has reamers 23 a and 23 b and propellers 24 a and 24 b inconnection with the reamers 23 a and 23 b, similarly to the vessel 10shown in FIGS. 1A and 1B.

FIGS. 4A and 4B show the ship 30 shown in FIGS. 2A and 2B, and thedetachable bow section 31 shown in FIGS. 3A and 3B as attached to oneanother. FIGS. 4A and 4B illustrate that the ship 30 and the detachablebow section 31 form, as attached to one another, an icebreaking vessel10 corresponding to what is shown in FIGS. 1A and 1B. If the strengthsand engine outputs of the ship 30 and the detachable bow section 31 aresufficient, this icebreaking combination vessel 10 is capable of taskscomparable to those of the icebreaking vessel 10 shown in FIGS. 1A and1B. It can also be equally effective and agile while manoeuvring in ice.

FIGS. 5A and 5B show an icebreaking vessel 10 corresponding to thevessel in FIGS. 1A and 1B. In the vessel 10 shown in FIGS. 5A and 5B,however, the propellers 24 a and 24 b in connection with the reamers 23a and 23 b are positioned in azimuthing thruster apparatuses 28 a and 28b. Even though traditional fixed propeller shafts work very well in avessel according to the invention, azimuthing thruster apparatuses dohave some advantages over fixed shafts.

An advantage of thruster apparatuses is that they leave a larger spacefor pieces of ice compared with fixed shafts. In some cases pieces ofice may become wedged between the hull and the strut of a fixed shaft.In a thruster apparatus, the propeller shaft can also be directedupwards, whereby the propeller pushes water and pieces of ice upwardsalong the side of the hull. If a propeller is positioned ahead of thethruster apparatus, the propeller of such a pulling thruster apparatusoperates in a clear water flow with no disturbance due to turbulencesfrom the pod of the thruster apparatus. The propeller of a pullingthruster apparatus also effectively breaks up pieces of ice, wherebythey will not become wedged anywhere.

According to the invention, all possible propeller configurations can beused in the thruster apparatuses positioned in connection with thereamers. There can thus be a single or two pulling propellers ahead ofthe thruster apparatus, there can a single or two pushing propellersastern of the thruster apparatus, and a single or two propellers bothahead and astern of the thruster apparatus.

FIGS. 6A, 6B, 7A and 7B show a ship 30 to which can be attached adetachable bow section 31 according to the invention. The detachable bowsection 31 has in connection with reamers 23 a and 23 b azimuthingthruster apparatuses 28 a and 28 b. FIGS. 8A and 8B show the ship 30 andthe detachable bow section 31 as attached to one another, which createsan effective icebreaking vessel 10 according to the invention.

FIGS. 9A and 9B show a schematic view of an icebreaking vessel 10according to the invention where both thruster apparatuses 28 a and 28 bin connection with reamers 23 a and 23 b are pivoted outwards, i.e. tothe sides. As the vessel 10 proceeds ahead and breaks ice, the pullingthruster apparatuses 28 a and 28 b at the sides of the vessel 10 can bepivoted slightly outwards. Thereby the flow of water created bypropellers 24 a and 24 b is directed to the edge of ice at the sides ofthe vessel 10, breaking it up, as a consequence of which the ice channelbroken by the vessel 10 becomes wider. In such a situation, the pivotangle required for the thruster apparatuses 28 a and 28 b does notnecessarily have to be large. Due to the characteristics of the thrusterapparatuses 28 a and 28 b, however, both propellers 24 a and 24 b can bedirected, either simultaneously or independently of each other, alsodirectly to the side and even ahead as required. By using various anglesand power settings of the thruster apparatuses 28 a and 28 b, it ispossible to have the vessel either widen up the ice channel, proceed inany required direction or turn around in place.

FIG. 10A shows a schematic back view of the icebreaking vessel 10 inFIG. 8A wherein a detachable bow 31 according to the invention isattached to a ship 30. In connection with the reamers 24 a and 24 b atthe sides of the detachable bow 31, there are azimuthing thrusterapparatuses 28 a and 28 b equipped with propellers 24 a and 24 b. FIG.10A clearly illustrates that, thanks to the detachable bow 31, the bowsection of the vessel 10 becomes relatively wide, whereby the vessel 10is capable of breaking up a wide ice channel. FIG. 10A furthermore showsthat the distance between the propellers 24 a and 24 b in connectionwith the reamers 23 a and 23 b located at the sides of the detachablebow 31 on the transverse direction of the vessel 10 is large. As aconsequence of this, the thruster apparatuses 28 a and 28 b located farapart from each other form a large torque axis, by means of which it ispossible to create a very large torque resulting in a turning action onthe vessel 10. When the power settings of the thruster apparatuses 28 aand 28 b or corresponding fixed propellers are adjusted independently ofeach other, or the propellers 24 a and 24 b are rotated in differentdirections, the vessel 10 will easily turn as required, thanks to thelarge torque, or proceed in the required direction.

FIG. 10B shows a situation where the thruster apparatuses 28 a and 28 bof the vessel in FIG. 10A are pivoted towards the sides of the vessel10. Even a small pivot angle of the thruster apparatuses 28 a and 28 bwill direct the flow of water towards the edges of ice on the sides,whereby the ice channel widens up. A further advantage of the thrusterapparatuses 28 a and 28 b, in addition to easily manoeuvring turns, isthat the thruster apparatuses 28 a and 28 b can be tilted both in thelongitudinal and transverse direction of the vessel 10, whereby the flowof water under the hull is directed along the hull shape. A preferredtilt of 3°-10° relative to the vertical plane of the thrusterapparatuses 28 a and 28 b, for example, will pivot the propeller shaftsfor an equal distance, whereby the propellers 24 a and 24 b will directthe flow of water upwards along the hull shell. This has an advantageouseffect on an icebreaking vessel because, in addition to the widening ofthe ice channel, the flow of water will push away the pieces of ice fromunder the hull and the sides.

LIST OF REFERENCE NUMBERS

-   10 Icebreaking vessel-   20 Bow section-   21 Stern section-   23 a Reamer-   23 b Reamer-   24 a Propeller-   24 b Propeller-   24 c Propeller-   25 a Propeller shaft-   25 b Propeller shaft-   26 a Motor-   26 b Motor-   27 Thruster apparatus-   28 a Thruster apparatus-   28 b Thruster apparatus-   30 Ship-   31 Detachable bow section

1. An icebreaking vessel (10) with reamers (23 a, 23 b) at each side,characterized in that, in connection with the reamers (23 a, 23 b)located at each side of the icebreaking vessel (10), there arepropellers (24 a, 24 b) for the propulsion of the vessel.
 2. A vessel(10) according to claim 1, characterized in that there are downwardsbreaking reamers (23 a, 23 b) at each side of the vessel (10) and thepropellers (24 a, 24 b) in connection with them are located in themidship area of the vessel, or between the midship and the bow of thevessel.
 3. A vessel (10) according to claim 1 or 2, characterized inthat the propellers (24 a, 24 b) in connection the reamers (23 a, 23 b)located at each side of the vessel (10) are attached to propeller shafts(25 a, 25 b) directed towards the stern of the vessel, the propellersshafts being horizontal or tilted downwards or upwards, and thepropellers shafts being parallel as viewed from above or directedslightly outwards, towards the sides of the vessel, or inwards, suchthat the propeller shafts form an angle relative to one another.
 4. Avessel (10) according to claim 1 or 2, characterized in that thepropellers (24 a, 24 b) in connection the reamers (23 a, 23 b) locatedat each side of the vessel (10) are attached to either fixed orazimuthing thruster apparatuses (28) which have one or two pullingpropellers ahead of the thruster apparatus, or one or two pusherpropellers astern of the thruster apparatus, or at least one propellerahead of the thruster apparatus and at least one propeller astern of thethruster apparatus.
 5. A vessel (10) according to any one of claims 1-4,characterized in that the vessel (10) has propellers (24 a, 24 b) inconnection with the reamers (23 a, 23 b) located at the sides of thevessel (10) only.
 6. A vessel (10) according to any one of claims 1-4,characterized in that, in addition to the propellers (24 a, 24 b) inconnection with the reamers (23 a, 23 b) located at the sides of thevessel (10), the vessel has at least a single propeller (24 c) and/orthruster apparatus (27) in the stern.
 7. A vessel (10) according to anyone of claims 1-6, characterized in that, the inclination of the hullsides relative to the vertical plane in the bow section of the vessel(10) is greater than 10° at the point where the hull sides of the shipcome into contact with the ice to be broken.
 8. A vessel (10) accordingto any one of claims 1-7, characterized in that, in the icebreakingvessel (10), the draught of the bow section (20) equipped with reamers(23 a, 23 b) and propellers (24 a, 24 b) is equal to or larger orsmaller than the draught of the stern section (21) of the vessel.
 9. Avessel (10) according to any one of claims 1-8, characterized in thatthe icebreaking vessel (10) equipped reamers (23 a, 23 b) located at thesides and propellers (24 a, 24 b) in connection with them has beenarranged by attaching to a ship (30) which is not an actual icebreakersuch a detachable icebreaking bow section (31) that has reamers (23 a,23 b) at the sides and propellers (24 a, 24 b) in connection with them.10. A vessel (10) according to any one of claims 1-9, characterized inthat the icebreaking vessel (10) is comprised of a ship (30), such as amerchant ship or a cargo ship, to which can be attached a detachableicebreaking bow section (31) with reamers (23 a, 23 b) at each side andpropellers (24 a, 24 b) in connection with them.
 11. A vessel (10)according to any one of claims 1-10, characterized in that the totalengine power of the propellers (24 a, 24 b) in connection with thereamers (23 a, 23 b) of a detachable icebreaking bow section (31) isgreater than or equal to the engine power of the propeller or propellersof the ship (30) to be attached to the detachable bow section.
 12. Avessel (10) according to any one of claims 1-11, characterized in thatthe detachable icebreaking bow section (31) equipped with reamers (23 a,23 b) located at the sides and with propellers (24 a, 24 b) inconnection with the reamers can be attached to the ship (30) whenbreaking ice is necessary or when the ship is heading to ice-coveredwater areas, and can be detached from the ship when the ship is used inopen water areas.
 13. A vessel (10) according to any one of claims 1-12,characterized in that, in the icebreaking vessel (10), the draught ofthe detachable bow section (31) equipped with reamers (23 a, 23 b) andpropellers (24 a, 24 b) is equal to or larger or smaller than thedraught of the ship (30) to be attached to it.
 14. A vessel (10)according to any one of claims 1-13, characterized in that thepropulsion system of the detachable icebreaking bow section (31) of theicebreaking vessel (10) includes parts such as an electric motor,generator, diesel engine and the fuel tank of the diesel engine, whichare distributed and positioned such that some of the said parts arelocated in the detachable icebreaking bow section (31) and some in thevessel (30).
 15. A vessel (10) according to any one of claims 1-14,characterized in that the detachable icebreaking bow section (31)equipped with reamers (23 a, 23 b) and propellers (24 a, 24 b) inconnection with them has joint members to attach the detachable bowsection to any ship (30), such as a merchant ship or a cargo ship, whichhas corresponding joint members for attaching the detachable bow sectionto the ship.
 16. A vessel (10) according to any one of claims 1-15,characterized in that the icebreaking vessel (10) is arranged by thedetachable icebreaking bow section (31) equipped with reamers (23 a, 23b) and propellers (24 a, 24 b) in connection with them and any ship(30), such as a merchant ship or a cargo ship, that can be selected froma group of one or several such ships where the ships belong to thesegroups have joint members for attaching the detachable bow section tothe ship.
 17. A vessel (10) according to any one of claims 1-16,characterized in that the icebreaking vessel (10) is arrangedalternatingly by at least two ships (30), such as a merchant ship or acargo ship, with joint members for alternatingly attaching thedetachable icebreaking bow section (31) equipped with reamers (23 a, 23b) and propellers (24 a, 24 b) in connection with them.